1. Field of the Invention
The present invention relates to a rechargeable battery, and more particularly, to a rechargeable battery having an improved welding structure and a method of manufacturing the rechargeable battery
2. Description of the Related Art
Unlike a primary battery, a rechargeable battery may be recharged. Recently, a high output rechargeable battery using non-aqueous electrolyte having a high energy density has been developed. Low capacity rechargeable batteries are used for various portable electronic devices such as phones, laptop computers, and camcorders. High capacity rechargeable batteries formed by connecting a plurality of low capacity rechargeable batteries in series or parallel are used to drive motors, such as those of hybrid electric vehicles.
Depending on their external shape, rechargeable batteries may be classified into different types, for example, prismatic and cylindrical batteries. The rechargeable battery includes an electrode assembly having positive and negative electrodes and a separator interposed between the positive and negative electrodes, a case for receiving the electrode assembly, a cap assembly for sealing the case, and positive and negative terminals extending from the cap assembly and electrically connected to the positive and negative electrodes, respectively.
A cap plate of the cap assembly is attached on the case by welding to maintain an airtightness of the case. The welding may be performed vertically (i.e., essentially perpendicular to the weld joint) when the cap plate is fitted in the case or performed horizontally (i.e., essentially parallel to the weld joint) when the cap plate lays on a top surface of the case.
Tolerance variations may arise during the manufacturing process of the cap plate and the case. As a result, it may be difficult to vertically weld together the cap plate and the case. For example, in order to vertically weld together the cap plate and the case, the cap plate must be precisely fitted to an inner circumference of the case. However, when there are tolerance variations in the cap plate and/or the case, a gap may be created between the inner circumference of the case and the outer circumference of the cap plate. This may cause poor welding. Furthermore, laser beams generated during welding may reach the electrode assembly through the gap, damaging the electrode assembly.
When welding is performed horizontally with the cap plate laying on the top surface of the case, a gap may be also created between the top surface of the case and the cap plate due to the tolerance for error of the case and/or the cap plate. Similarly, the laser beams may be emitted to the electrode assembly through the gap, thereby damaging the electrode assembly. The welding defect between the cap plate and the case deteriorates the service life and performance of the rechargeable battery and may cause the rechargeable battery to be unusable.